Man page - gmx-dielectric(1)

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Manual

GMX-DIELECTRIC

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
SEE ALSO
COPYRIGHT

NAME

gmx-dielectric - Calculate frequency dependent dielectric constants

SYNOPSIS

gmx dielectric [ -f [<.xvg>] ] [ -d [<.xvg>] ] [ -o [<.xvg>] ] [ -c [<.xvg>] ]
[ -b <time> ] [ -e <time> ] [ -dt <time> ] [ -[no]w ]
[ -xvg <enum> ] [ -[no]x1 ] [ -eint <real> ] [ -bfit <real> ]
[ -efit <real> ] [ -tail <real> ] [ -A <real> ] [ -tau1 <real> ]
[ -tau2 <real> ] [ -eps0 <real> ] [ -epsRF <real> ]
[ -fix <int> ] [ -ffn <enum> ] [ -nsmooth <int> ]

DESCRIPTION

gmx dielectric calculates frequency dependent dielectric constants from the autocorrelation function of the total dipole moment in your simulation. This ACF can be generated by gmx dipoles . The functional forms of the available functions are:

One parameter: y = exp(-a_1 x),

Two parameters: y = a_2 exp(-a_1 x),

Three parameters: y = a_2 exp(-a_1 x) + (1 - a_2) exp(-a_3 x).

Start values for the fit procedure can be given on the command line. It is also possible to fix parameters at their start value, use -fix with the number of the parameter you want to fix.

Three output files are generated, the first contains the ACF, an exponential fit to it with 1, 2 or 3 parameters, and the numerical derivative of the combination data/fit. The second file contains the real and imaginary parts of the frequency-dependent dielectric constant, the last gives a plot known as the Cole-Cole plot, in which the imaginary component is plotted as a function of the real component. For a pure exponential relaxation (Debye relaxation) the latter plot should be one half of a circle.

OPTIONS

Options to specify input files:
-f [<.xvg>] (dipcorr.xvg)

xvgr/xmgr file

Options to specify output files:
-d [<.xvg>] (deriv.xvg)

xvgr/xmgr file

-o [<.xvg>] (epsw.xvg)

xvgr/xmgr file

-c [<.xvg>] (cole.xvg)

xvgr/xmgr file

Other options:
-b <time> (0)

Time of first frame to read from trajectory (default unit ps)

-e <time> (0)

Time of last frame to read from trajectory (default unit ps)

-dt <time> (0)

Only use frame when t MOD dt = first time (default unit ps)

-[no]w (no)

View output .xvg , .xpm , .eps and .pdb files

-xvg <enum> (xmgrace)

xvg plot formatting: xmgrace, xmgr, none

-[no]x1 (yes)

use first column as x -axis rather than first data set

-eint <real> (5)

Time to end the integration of the data and start to use the fit

-bfit <real> (5)

Begin time of fit

-efit <real> (500)

End time of fit

-tail <real> (500)

Length of function including data and tail from fit

-A <real> (0.5)

Start value for fit parameter A

-tau1 <real> (10)

Start value for fit parameter tau1

-tau2 <real> (1)

Start value for fit parameter tau2

-eps0 <real> (80)

epsilon0 of your liquid

-epsRF <real> (78.5)

epsilon of the reaction field used in your simulation. A value of 0 means infinity.

-fix <int> (0)

Fix parameters at their start values, A (2), tau1 (1), or tau2 (4)

-ffn <enum> (none)

Fit function: none, exp, aexp, exp_exp, exp5, exp7, exp9

-nsmooth <int> (3)

Number of points for smoothing

SEE ALSO

gmx(1)

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COPYRIGHT

2025, GROMACS development team